The present invention relates to a semiconductor device and, more particularly, to an exposure apparatus.
A photolithography process uses a photomask with different patters to form patterns on a wafer. The photolithography process projects the patterns formed on the photomask onto a photoresist film deposited over the wafer by using an exposure apparatus. A development process is then applied to the photoresist film to form photoresist patterns on the wafer.
However, when the wafer is exposed during the photolithography process, light intensity which directly comes from an exposure light source can be different from light intensity projected on the wafer after the light passes through the photomask. For example, although the distribution of light intensity is uniform before the light emitted from the exposure light source passes through the photomask, the projected light intensity passing through the photomask is not uniform because of various optical phenomena of light passing through the photomask. Since the uniformity of light intensity is different at different positions of the photomask, line widths (CD) of the patterns formed on the wafer can be differently formed.
Also, the uniformity of the line widths of the patterns formed on the photomask affects the uniformity of circuit patterns formed on the wafer. Thus, the uniformity of the patterns of the photomask is very important. For example, if an exposure process of the wafer is performed by using the photomask having a low pattern uniformity, the intra-field uniformity of the wafer can also be lowered by such a low pattern uniformity of the photomask. Particularly, if the line widths of the patterns within the wafer field are asymmetrically non-uniform due to the pattern uniformity of the photomask and the uniformity of an exposure slit, a problem occurs in that a non-uniformity of the line widths of the wafer patterns cannot be corrected by the current exposure apparatus. Accordingly, studies of the line width correction of the wafer patterns have been conducted in case that the line widths of the patterns within the wafer field are asymmetrically non-uniform.